In the art of making a record member with drops of charged fluid, difficulty has been encountered in inducing the desired charge on a drop because of the drift in phase relationship between applied charging signals and the instant of drop formation when induced charges are created within the drop. The loss of synchronization between the applied charge and drop formation results in the drops attaining either insufficient or excessive charge and thus subsequently achieving an erroneous trajectory when subjected to an electrostatic deflection field. Misplaced drops on a receiving record member are noticeable and the printing thereon assumes a smudged or fuzzy appearance.
The customary corrections used to overcome the loss of synchronization have been to install sensors along the drop path or to use a multi-compartment sensing gutter for discarded drops and detect departure from some pre-established norm in electrical signal. The change in signal level is then used as an error signal to alter the phase relation between drop formation and charging. Corrections are made in drop formation time and location by altering fluid pressure or temperature. Charging signal timing is varied by changing electrical circuit delay by either analog or digital controls. These controls obviously add structure and complexity to the drop charging and forming apparatus.
A further difficulty experienced in marking with charged fluid drops is that of obtaining density control of the deposited liquid. Techniques to accomplish this have included variable dispersion of drops directed toward a recording surface through an opening in a shield. By producing a fine spray with variable dispersion there is control over the amount of marking fluid impacting the recording surface. This technique requires that the shield opening serve to limit or control the diameter of the formed mark.
Another technique is that of recording in small advancing increments between marking jet and rotating recording surface to enable selected drop placement in a matrical position. A varying number of these positions can be impacted through jet control to create the desired density effect.
Another technique is that of controlling the merging of formed drops in flight by establishing mutually atractive charges on adjacent drops. Drop merging requires complicated switching circuits in order to control the charging signal and to obtain the proper ultimate drop size. These techniques of density control necessitate either additional structure or complex data handling and storage arrangements, adding to the cost and at times impairing recording efficiency.
It is accordingly a primary object of this invention to provide a method of marking with charged drops of marking fluid in which synchronization between charging signals and drop formation is not required.
A further object of this invention is to provide a method of marking with charged drops in which a plurality of similarly charged drops are used to create a single mark on a recording surface.
Another important object of this invention is to provide a method of marking with charged drops in which each charging signal level induces similar charges on a plurality of successive drops.
A still further object of this invention is to provide a method of marking with charged drops of marking fluid in which the drop generation frequency is an integral multiple of the charging signal or data frequency.
A further object of this invention is to provide a method of marking with charged drops of fluid in which a range of density of marking fluid on a recording surface is attained by varying the number of successively and similarly charged drops impacting each predetermined recording area.